What materials make the strongest permanent magnets?

Traditional permanent magnets were made of an alloy of aluminum, nickel, and cobalt, called ALNICO. Ceramic and rubber magnets use ferrites, an iron oxide material. In the 1980s the automobile companies searched for materials to reduce the weight of motors in their cars. They found an alloy of cobalt and samarium, a rare earth, made strong, lightweight magnets, but were extremely brittle and expensive. Today the strongest magnets are made from a lanthanum-iron-boron (LIB) alloy. Their strength can be as much as 20 times that of alnico magnets. They are also brittle and so are coated with a plating of nickel and copper. Their price has fallen so much that they are used to hold sunglasses to eyeglass frames, in necklace clasps, and in children’s toys.


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